[PKop]

I think you underestimate the scale and magnitude of the industrial, steel, and auto industry dominance in some of these areas, and then the precipitous decline since.

https://en.wikipedia.org/wiki/Rust_Belt

“Before World War II, the cities in the Rust Belt region were among the largest in the United States. However, by the twentieth century's end their population had fallen the most in the country.”

Knowing nothing else about the particulars of why this was the case, it’s easy to see that this change would have drastic consequences for these areas.